1. Field of the Invention
The present invention relates to an apparatus for supplying a constant amount of abrasive, and more particularly, to an apparatus for supplying abrasive which is suitably used for supplying a constant amount of abrasive to a blast gun together with compressed gas in a blasting process in which abrasive is ejected from the blast gun together with compressed gas and blown and bombarded against a workpiece for processing the workpiece.
2. Description of the Related Art
In a blasting process in which abrasive is ejected from a blast gun together with compressed air for, for example, cutting, deburring, or cleaning a workpiece, any variation in the ejected amount of abrasive results in variation in the extent of processing, leading to uneven processing or the like with a resultant failure to uniformly maintain processing accuracy at a fixed level.
Thus, in order to eject a constant amount of abrasive at all times from a blast gun of a blasting machine, there is proposed an apparatus for merging a predetermined amount of abrasive with compressed gas and introducing the resultant mixed fluid to the blast gun so that a constant amount of abrasive can be ejected continuously and constantly from the blast gun.
Regarding one example of such an apparatus, the applicant of the present application has proposed an apparatus 100 shown in FIG. 7 (Prior Art).
The apparatus 100 shown in FIG. 7 (Prior Art) is configured as follows. A rotating disc 120 which rotates horizontally is provided within an abrasive tank 110 which is constructed as a pressure vessel. An opening at one end 111a of an abrasive transport path 111 is disposed close to or in contact with one surface of the rotating disc 120. An opening at one end 112a of an air introduction path 112 is disposed close to or in contact with another surface of the rotating disc 120 in such a manner as to face the opening at the one end 111a of the abrasive transport path 111. A plurality of measuring holes 121 are bored in the rotating disc 120 in such a manner as to pass therethrough in the thickness direction of the rotating disc 120 and in such a manner as to be disposed at equal intervals on a rotation orbit of the measuring holes 121 which passes between the opening of the abrasive transport path 111 and the opening of the air introduction path 112.
The rotating disc 120 having the measuring holes 121 bored therein is rotated at a constant speed. By this operation, abrasive contained in the abrasive tank 110 is charged into the measuring holes 121, and the abrasive contained in each of the measuring holes 121 reaches a clearance between the air introduction path 112 and the abrasive transport path 111. In the clearance, a compressed-air flow from the air introduction path 112 to the abrasive transport path 111 acquires the abrasive from each of the measuring holes 121 and is mixed with the abrasive. The resultant two-phase fluid composed of solid and gas is supplied to a blast gun.
The abrasive to be supplied to the blast gun as mentioned above is charged into the measuring holes 121 provided in the rotating disc 120, thereby being measured in a constant amount. Thus, by means of varying the rotational speed of the rotating disc 120, the amount of supply of abrasive to the blast gun can be varied. When the rotating disc 120 is maintained at a constant rotational speed, a constant amount of abrasive can be constantly supplied to the blast gun (refer to Japanese Unexamined Patent Publication Nos. 2008-264912 and 2009-208185).
The apparatus 100 described above with reference to FIG. 7 (Prior Art) is excellent in the following points: the amount of supply of abrasive can be varied easily through control of the rotational speed of the rotating disc 120, and abrasive can be supplied in a constant amount with high accuracy.
The apparatus 100 described above with reference to FIG. 7 (Prior Art), however, has a structure in which abrasive charged beforehand in the abrasive tank 110 constructed as a pressure vessel is ejected by means of the internal pressure of the abrasive tank 110, so that during blasting work the abrasive tank 110 cannot be replenished with abrasive. Therefore, before blasting work is started, the abrasive tank 110 must be charged with a predetermined amount of abrasive.
Thus, the apparatus 100 cannot supply, for example, dry ice particles, ice particles, or the like in a constant amount, since if such particles are left in a heap, the particles adhere to one another to form lumps by the effect of, for example, moisture in air, resulting in a failure to charge the measuring holes 121 with the particles.
FIG. 8 exemplifies a conceivable configuration for using dry ice particles or ice particles as abrasive. Specifically, an abrasive charge section 230 is provided for allowing abrasive to fall therethrough without application of pressure so as to charge the abrasive into the measuring holes 221 of the rotating disc 220. Thus, a required amount of abrasive is introduced appropriately and continuously into the abrasive charge section 230 without involvement of stacking of abrasive for a long period of time, thereby charging the measuring holes 221 of the rotating disc 220 with abrasive.
In the case where the structure of the abrasive charge section 230 has been modified as mentioned above, if one end 212a of an air introduction path 212 and one end 211a of an abrasive transport path 211 with the rotating disc 220 intervening therebetween are not disposed within a pressure vessel, as shown in FIG. 8, compressed air and abrasive leak out through rotation allowance clearances δ between the front surface of the rotating disc 220 and the one end 212a of the air introduction path 212 and between the back surface of the rotating disc 220 and the one end 211a of the abrasive transport path 211. Therefore, the abrasive cannot be supplied in a constant amount.
In the apparatus 100 described above with reference to FIG. 7 (Prior Art), in order to ensure smooth rotation of the rotating disc 120, the rotation allowance clearances δ are provided between the one end 112a of the air introduction path 112 and the front surface of the rotating disc 120 and between the one end 111a of the abrasive transport path 111 and the back surface of the rotating disc 120. Even though the rotation allowance clearances δ are provided, compressed air in the air introduction path 112 and a mixed fluid in the abrasive transport path 111 do not leak out through the rotation allowance clearances δ to the exterior of the apparatus 100, since the region associated with the clearances δ is accommodated within the pressurized abrasive tank 110.
However, in the configuration of FIG. 8 in which the one end 212a of the air introduction path 212 and the one end 211a of the abrasive transport path 211 with the rotating disc 220 intervening therebetween are not disposed within a pressure vessel, a high-pressure compressed gas introduced from a compressed-gas supply source leaks out to the ambient atmosphere through the rotation allowance clearance δ between the surface of the rotating disc 220 and each of the air introduction path 212 and the abrasive transport path 211. Accordingly, not only does the pressure of the compressed gas to be supplied to the blast gun drop greatly, but also the abrasive leaks out in association with the leakage of the compressed gas. As a result, a work environment is contaminated with the abrasive, and the amount of abrasive to be supplied to the blast gun reduces, with a resultant failure in constant supply of abrasive in a constant amount.
In view of these circumstances, the present invention was made to overcome problems associated with the above-described existing techniques. An object of the present invention is to provide an apparatus for constantly supplying a constant amount of abrasive in which abrasive is mixed with a compressed gas for supplying the resultant two-phase fluid composed of solid and gas and which, even in the case of a rotating disc being disposed outside an abrasive tank, can supply a constant amount of abrasive at all times without involvement of leakage of the compressed gas, and thus can supply even dry ice particles, ice particles, or the like as abrasive, in addition to ordinary abrasives, in a constant amount.